Molecular Signaling and Cellular Cross-Talk to Tackle Metal(loid) Stress: Decoding Plants’ Secret Saga of Survival

Environmental contamination by heavy metals and metalloids is a serious problem globally, which endangers the environmental quality and ecosystem health. The concentrations of toxic metal(loid)s (TMs) such as Hg, As, Cd, Cu, Cr, Co have been rising in soil, water, and air due to diverse anthropogenic activities such as industrialization, mining, urbanization, and chemical-intensive agriculture. The potential adverse effects on organisms are caused due to their nonbiodegradability, persistence, bioaccumulation, and toxicity above admissible levels. The TMs adversely affect plants’ physiology, metabolism, growth, development, and senescence. To cope with the TMs stress and survive under such stressful environment, plants have evolved intricate signaling systems that sense, analyze, and transmit stress signals. When plants encounter TMs, oxidative stress is resulted in the cells, and the production of characteristic proteins, stress-related hormones, antioxidants, and a suite of signaling molecules are started. This chapter highlights the functions of phytohormones, phytochelatins, metallothionines, amino acids, and organic acids while summarizing the key mechanisms and signaling pathways of plants under metal(loid) stress, including calcium dependent, mitogen activated protein kinase (MAPK), reactive oxygen species (ROS), miRNA, their signaling crosstalk, and ultimate impacts. In addition, the potential involvement of key phytohormones and other biochemicals in signal transductions and gene expressions to protect, tolerate, or lessen TM toxicity in plants is also discussed. The problems and prospects for further study in this field of signaling pathways under TMs stress are also presented.